Study On Contact Mechanics Properties And EHL Theory Of Rock-Bit Cylindrical Roller Bearing

In order to speed up the rate of oil & gas exploration and development, and improve the international competition of drilling engineering technology, improving the working performance and working life of bit especially the rock bit is very important. Currently the knowledge of contact mechanics, lubrication theory and other disciplines should be utilized to carry out in-depth research on some critical problems such as roller crowned design, hollow cylindrical roller and its lubrication status, thus researching and developing roller bearing rock bit with long life and high speed.Fist of all, by studying the solution method of Hertzian point contact problem, the accurate and efficient full numerical method was obtained. Through comparative study of calculation speed, calculation accuracy, and calculation convenience of some typical algorithms, the applicable condition of each algorithm under different conditions was obtained. And then full numerical method was applied to single-arc crowned roller in rock-bit roller bearing, to analyze the change of contact parameters under different conditions. Secondly, taking advantage of Finite Element software MSC. Marc, the stress distribution of common representative types of crowned roller so far were analyzed. It is put forward that the Lundberg theoretical logarithmic crowned type can be replaced approximately by multiple-variable-curvature arcs, and according to the theoretical research, the appropriate number of variable-curvature-arc segments were presented. And then the stress distribution of hollow as well as concave-ended hollow cylindrical roller was analyzed. It is shown that, the reasonable hollow ratio can reduce the contact stress concentration in the roller end, But it can not avoid the sharp edge equivalent stress, under the same hollow ratio, the change of equivalent stress and contact stress is different with the change of loads. The optimal hollow ratio is also different under different extrnal loads. The equivalent stress on the inner wall can exceed the corresponding value on the outer wall, thus making the inner wall be the dangerous area under large hollow ratio. The bending stress should be considered in the mean time to avoid the bending fatigue failure occurred on the inner wall of roller. Compared with ordinary hollow roller, concave-ended hollow cylindrical roller can effectively overcome the stress concentration at the end of roller. Finally, the multilevel method was utilized to analyze the elastohydrodynamic lubrication (EHL) condition of solid as well as hollow cylindrical roller in rock bit. The analysis of EHL for infinite line contact illustrated that the change of film pressure and thickness under different load parameters, velocity parameters, and material parameters. The change of hollow ratio for hollow cylindrical roller can cause the change of velocity parameter and load parameter, but will not cause the obvious change of film thickness and minimum film thickness at central contact area. The increase of hollow ratio can reduce the film pressure, but the stress distribution on inner wall should be considered when selecting a reasonable hollow ratio. The analysis of EHL for finite line contact showed that, the maximum film pressure and minimum film thickness were both at the end of roller, therfore the end of roller is the easily damaged area. The lubrication condition at middle part of the roller can be treated as infinite, due to its similarity to the infinite one. At the end part and middle part of roller, the influence of hollow ratio on lubrication condition was the same. Because the film pressure at the end was larger than that at the middle, the second peak and minimum film thickness were both closer to inlet-zone.The research results established a solid foundation for accomplishing the long-life and high-speed of rock bit with roller bearing, furthemore it can be used to improve the working performance of heavy-load and low-speed roller bearing system widely existed in engineering practice. It is also worth to be learne by the researchers in standard or universal roller bearing, railway locomotive, metallurgical mill and so on.